Problem 2813. Create a block diagonal matrix

A block diagonal matrix is a square matrix that can be written as

   A = [a  0  0  0
        0  b  0  0
        0  0  c  0
        0  0  0 ...]

where a, b, c etc. are all square matrices.

Construct A such that

   A = [a  0  0  0
        0  a  0  0
        0  0  a  0
        0  0  0 ...]

where a is allowed to be non-square or empty and occurs n times. n is always an integer greater than or equal to 0.

Examples:

   a = [1 2 3], n = 3

gives

   A = [1 2 3 0 0 0 0 0 0
        0 0 0 1 2 3 0 0 0
        0 0 0 0 0 0 1 2 3]